As cellular phones and information terminals have been advanced, image display devices become smaller and finer. On the other hand, as new value-added image display devices, attention has been drawn to image display devices allowing an observer to view different images depending on an observing point, namely image display devices with which different images are visible at multiple observing points, and to three-dimensional image display devices displaying different images as parallax images so that the observer can view a three-dimensional image.
A known technique of providing different images to multiple observing points merges and displays image data for different observing points on a display panel, separates the displayed composite image by an optical separating unit such as a lens and a barrier having slits (screen), and provides the images to individual observing points. The images can be separated by an optical unit such as a barrier having slits and a lens so as to limit the pixels to be seen from each observing point. A parallax barrier comprising a barrier having many slits in a stripe pattern or a lenticular lens comprising an array of cylindrical lenses having lens effect in one directional is generally used as the image separating unit.
A three-dimensional image display device employing an optical image separating unit is suitable for installing in terminal devices such as cellular phones because it does not require an observer to wear special glasses and eliminates annoyance of wearing glasses. Cellular phones carrying a three-dimensional display device comprising a liquid crystal panel and a parallax barrier have already been commercialized (for example, see “NIKKEI Electronics, No. 838,” Nikkei Publishing, Jan. 6, 2003, pp 26-27).
The above technique, namely a three-dimensional image display device providing different images to multiple observing points using an optical separating unit sometimes causes an observer to see a dark boundary between images as his/her observing point is shifted and the viewed image is switched. This phenomenon occurs when a non-display region between pixels for different observing points (a shielding unit generally called a black matrix in a liquid crystal panel) is viewed. This phenomenon accompanying shift of the observing point of the observer does not occur with a general three-dimensional display device without an optical separating unit. Therefore, the observer experiences discomfort or senses deterioration in the display quality from the above phenomenon occurring with a multiple observing point three-dimensional display device or three-dimensional display device with an optical separating unit.
This is a phenomenon generally called 3D moire. The 3D moire is a periodically appearing uneven luminance (sometimes referred to as uneven color) caused by displaying different images in different angular directions. Furthermore, the 3D moire is luminance angular fluctuation and large luminance angular fluctuation has adverse effect on three-dimensional observation.
In this specification, periodically appearing uneven luminance (sometimes referred to as uneven color) caused by displaying different images in different angular directions, particularly luminance angular fluctuation is defined as “3D moire.” Generally, fringes appearing when structures different in periodicity interfere with each other are called “moire fringes.” The moire fringes are interference fringes appearing depending on the periodicity or pitch of structures. On the other hand, the 3D moire is uneven luminance caused by the image-forming property of an image separating unit and seen from a specific position. Therefore, the 3D moire is distinguished from the moire fringes in this specification.
In order to ameliorate the above problem caused by an optical separating unit and shielding unit, three-dimensional image display devices in which the shape and geometry of pixel electrodes and shielding unit of the display panel is designed to reduce deterioration in the display quality have been proposed (for example, Unexamined Japanese Patent Application KOKAI Publication No. 2005-208567; Patent Literature 1, hereafter and Unexamined Japanese Patent Application KOKAI Publication No. H10-186294; Patent Literature 2, hereafter).
In the display device disclosed in the Patent Literature 1, as shown in FIG. 33, in a cross-section of the display panel in the vertical direction 1011 perpendicular to the direction of the array of cylindrical lenses 1003a, the ratio between the shielding unit (the wiring 1070 and shielding unit 1076) and aperture is nearly constant at any point in the horizontal direction 1012.
Therefore, even if the observer shifts his/her observing point in the horizontal direction 1012, which is the image separation direction, so as to change the observing direction, the ratio of the shielding unit viewed is nearly constant. In other words, it does not happen to the observer to see only the shielding unit in a specific direction or to see a darker display. Then, deterioration in the display quality caused by the shielding region is prevented.
The three-dimensional display device disclosed in the Patent Literature 2 has the pixel layout as shown in FIG. 34A and pixels as shown in FIG. 34B. In the three-dimensional display device disclosed in the Patent Literature 2, the total aperture width in the Y-axis direction of adjacent pixels is constant throughout an overlapping region 1013 and equal to the aperture width in the Y-axis direction in a rectangular region B. Therefore, the three-dimensional display device disclosed in the Patent Literature 2 can provide substantially uniform luminance continued in the horizontal direction and maintain substantially constant luminance in the X-axis direction.
Therefore, when the same image is output to adjacent columns of pixels, the three-dimensional display device disclosed in the Patent Literature 2 can maintain constant luminance while the observer's line of sight crosses the boundary between windows.
In prior art three-dimensional image display devices, pixel structures in which the aperture width is constant or nearly constant in the image separation direction as described above have been proposed. However, it was found that some production problems with the image separating unit leads to some issues on the three-dimensional display performance when the pixel structures disclosed in the Patent Literature 1 and Patent Literature 2 are used. The details are as follows.
Three-dimensional image display devices conventionally employ the above-mentioned parallax barrier or lenticular lens as a unit for optically separating images. A prior art lenticular lens has a periodically repeated structure in which the convex parts of cylindrical lenses and the concave parts between cylindrical lenses are adjacent to each other. Techniques for producing such a lenticular lens include molding using a die, photolithography, and inkjet.
However, with any technique being applied to production, there will be difference in processing accuracy between the convex part and concave part of a lens. Particularly, with a prior art lenticular lens, it is easier to produce the convex part in a given shape in a stable manner than the concave part. Then, the concave part is subject to deterioration in optical separation performance. For example, in the case of molding a lens using a die, the die is steeper and pointed in shape at the lens concave part than at the lens convex part. Not only the shape stability during molding but also the pressurizing during shaping contributes to the concave part having a lower level of shape stability than the convex part. Furthermore, even when a wet process such as an IJ technique is used to create a lens, the droplet boundary corresponds to the concave part and it is difficult to ensure the shape stability. Additionally, various factors including difficulty of removing unpeeled residues and/or adherent foreign substances from the lens concave part compared with from the lens convex part cause local deterioration in optical separation performance at the concave part.
In the region where the optical separation performance is deteriorated as described above, light emitted from the aperture of a pixel cannot be controlled by the image separating unit. Light emitted from the image separating unit under no control of the image separating unit results in a video image for one observing point being mixed with a video image for another observing point, which adversely affects the three-dimensional display. Particularly, when a mixture ratio between a video image for one observing point and a video image for another observing point exceeds a given value, the observer feels discomfort and has difficulty in three-dimensional observation. Furthermore, as the region of which three-dimensional observation is difficult because of mixture of a video image for one observing point and a video image for another observing point is enlarged, the proper three-dimensional observation range is narrowed; the three-dimensional display performance is lowered. Therefore, in this specification, mixture or leakage of a video image for one observing point and a video image for another observing point is defined as “3D crosstalk.” In this specification, the term “crosstalk” is used to refer to deterioration in the image quality due to electric leakage of video image signals and/or scan signals and distinguished from the “3D crosstalk.”
Among other optical separating unit, there is a GRIN (gradient index) lens, which is an electro-optic element using liquid crystal. Even with the use of a GRIN lens, the refractive index profile is more uneven at the lens concave part than at the lens convex part because of the relationship between electrode positions and electric field. Therefore, like the above-described lenticular lens, the optical separation performance at the lens concave part deteriorates.
Even with the use of a parallax barrier having slits, if the accuracy of processing the electrode end forming slits largely varies, the shielding performance at the slit end will become more uneven. Consequently, the image separation performance locally deteriorates, lowering the image quality.
Hence, it is difficult not only for a lenticular lens but also for any known image separating unit to achieve uniform optical separation performance. It is costly to obtain an image separating unit having completely uniform optical separation performance with the use of highly accurate processing techniques. When the pixels disclosed in the Patent Literature 1 and Patent Literature 2 in which the aperture width is constant in the image separation direction are used, some profile of optical separation performance of the image separating unit disturbs control over 3D moire and 3D crosstalk, deteriorating the three-dimensional display performance. Light delivered by high optical separation performance regions will easily be subject to 3D moire due to slight variation in the processing accuracy. Light delivered by low optical separation performance regions will be responsible for increased 3D crosstalk, narrowing the three-dimensional observation range. In regard to the above problems caused by the optical separation performance profile of the optical separating unit and the pixel structure, the techniques disclosed in the Patent Literature 1 and Patent Literature 2 encounter difficulty in accomplishing a design controlling both 3D moire and 3D crosstalk, failing to control both 3D moire and 3D and balance them.
The 3D moire may not be a problem at some observation positions. However, large luminance angular fluctuation presumably has some adverse effect on three-dimensional observation. Therefore, it is desirable that the fluctuation in luminance is equal to or lower than a given value. Furthermore, it is desirable that the magnitude of 3D crosstalk is equal to or lower than a given value.